Graphene films of controllable thickness as binder-free electrodes for high performance supercapacitors

Graphene films (G films) were obtained by direct vacuum filtration of a highly dispersed graphene suspension (G suspension) on filter paper. After the complete removal of the filter paper, the stand-alone G films were directly used as electrodes for supercapacitors, without any binder or electrochemical active additives. The thicknesses of the G films were controlled by varying the volume of filtrated G suspension. The stable G suspension was prepared by chemically reducing the graphite oxide together with the aryl diazonium salt solution. A small amount of charged sulphonate groups introduced by this process can effectively prevent the graphene nanosheets from aggregating during reduction. It was found that the best performing thin G film exhibited a high capacitance of 117.9 F/g at a high scan rate of 1000 mV/s, with no deterioration observed after 15,000 cycles at this scan rate, and its energy density reached 16.38 Wh/Kg when the highest power density was 58.97 KW/Kg at the high scan rate. (C) 2014 Elsevier Ltd. All rights reserved.